There are many products sold today—in supermarkets, mini-marts, vending machines, and in other non-food related retail locations—that require the use of packaging, other than a cardboard box, where the packaging may preferably be flexible and be sealed to be air-tight or liquid-tight. Such packaging is commonly made of a plastic film. Today, such films may typically be made from one or more of the following materials: polyethylene (PA); low, medium or high density polypropylene (LLDPE, LDPE, MDPE, or HDPE); polypropylene (PP), cast polypropylene (CPP), and oriented polypropylene (OPP); polyimide (PA); polyester (linear ester plastics); a polyethylene (PE) such as polyethylene terephthalate (PET); Polyvinylchloride (PVC); polyvinylidene chloride (PVDC); cellulose acetate (CA); cellophane; and aluminum (Al).
Machines for taking rolls of these films and shaping/creating a package, filling it with a pre-set amount of product, sealing the package, and separating successive packages in a continuous process are known in the art as form and fill packaging machines. There are generally two types—a vertical form-fill-sealing (VFFS) machine and a horizontal form-fill-sealing (HFFS) machine.
In the past, many of those thermoplastic materials (or thermo-softening plastics) had been joined to create a package by sealing through the direct application of heat to fuse adjoining sheets, typically in a lap or fin joint. An improvement was made in the sealing process by the introduction of ultrasonic welding techniques, which can be faster, and do not have some of the disadvantages of heat sealing, such as the potential for damage to the packaging material or product due to an excessive application of heat.
Ultrasonic welding techniques comprise the joining of similar or dissimilar material(s) by passing the material(s) between an anvil and a sonotrode, which is often referred to as a horn. The sonotrode may generally be connected to either a magnetostrictive transducer or a piezoelectric transducer. A magnetostrictive transducer uses electrical power to generate an electro-magnetic field that may cause the magnetostrictive material to vibrate. With a piezoelectric transducer, the supplied electrical power is directly converted, and more efficiently converted, into longitudinal vibrations. Use of the piezoelectric transducer reduces the cooling requirements, which result from the generation of the heat, which is a byproduct of the friction. The frequencies used in ultrasonic welding are typically in the range of 15 kHz to 70 kHz, and use of such frequencies causes local melting of the thermoplastic material due to absorption of heat generated from the vibration energy.
One of the earlier U.S. patents granted for ultrasonic welding was U.S. Pat. No. 2,946,119 to Jones for “Method and Apparatus Employing Vibratory Energy for bonding Metals,” while an early example of a machine utilizing ultrasonic welding principles is shown by U.S. Pat. No. 3,224,915 to Balamuth for “Method of Joining Thermoplastic Sheet Material by Ultrasonic Vibrations.” Balamuth cites improvement over the prior art, by inclusion of a rotary vibrator, which emits radial vibrations that are operative to join thermoplastic sheet materials being continuously advanced past the device. However, Balamuth does not disclose a complete VFFS or HFFS machine.
U.S. Pat. No. 4,288,965 to James does disclose a “Form-Fill-Seal Packaging Method and Apparatus,” in the form of a VFFS machine. The James VFFS machine pulls material from a roll, into a vertical tube for longitudinal seam sealing and product delivery, but advantageously requires a reduced amount of pull needed to form the package, thereby reducing tension in the material, along with its resultant degradation. The James VFFS machine represents an improvement over then expired U.S. Pat. No. 2,899,875 to Leasure titled “Apparatus for Packaging,” which had used a heated shoe to activate a heat sealing compound in order to create a tubular package. The James VFFS machine also enabled a relatively high rate of production of packages. Transverse sealing to create a top seal for a completed package and a bottom seal for a next package was accomplished using a pair of sealing bars operable in a horizontal plane, which may include an integral cutting means.
U.S. Pat. No. 4,517,790 to Kreager for “Apparatus and Method for Ultrasonic Sealing of Packages” provides improvements over prior art form-fill-seal machines which had generally featured intermittent motion in the discrete process steps of forming and filling, and then sealing. Kreager permitted transverse end sealing “on the fly,” meaning continuously. The Kreager machine “utilizes a rotary back-up anvil and a simulated rotary motion ultrasonic sealing horn in synchronism with one another,” to “provide an appropriate end seal for each package while on the move.”
There has been a long felt but unmet need, as to form-fill-seal machines, with respect to efficiency in the use of the film materials to create each package. When a consumer purchases a bag of chips or other product, a significant percentage of the cost of the purchase is attributable to the packaging. The major factors in determining the costs of the packaging are materials and labor. One of the ways to reduce the materials required for the package is to use a narrower ultrasonic weld to seal the package, and conserve the excess. There have been several inventions in related art, but they only peripherally address the issue.
U.S. Pat. No. 4,029,538 to Vance, Jr. for “Ultrasonic Film Splicer” stated that “The method of the instant invention comprises . . . binding said film strips together by applying oscillatory energy to the overlapped edges of the film strips by confining them between transducer means comprising a narrow elongated horn member . . . ” Similarly, U.S. Pat. No. 4,161,420 to Clarke for “Ultrasonic Method for Manufacturing Brassiere Tapes” taught having an anvil with a knife edge and beveled sections to “provide a comparatively narrow path responsive to the ultrasonic energy applied to the horn.” However, both of these inventions merely teach using a “narrow” anvil/horn combination to produce a narrow width of welded material, but offer nothing toward maintaining the integrity of the seal, which is crucially important for preserving product freshness, and when seeking to securely package liquids. The invention disclosed herein provides a means of producing a narrower weld to reduce the material costs of packaging, while simultaneously achieving weld integrity matching or exceeding that of the standard ultrasonic welding of existing form-fill-seal machines.